Rauwolscine hydrochloride is a potent and specific alpha2 adrenergic receptor antagonist with a Ki of 12 nM. IC50 & Target: Ki: 12 nM (alpha2 adrenergic receptor)[1]In Vitro: [3H]Rauwolscine binding to alpha2 adrenergic receptor is reversible, stcreospccific, and saturable. [3H]Rauwolscine specifically labels both the high and low affinity states of the alpha2 adrenergic receptor in brain membranes[1]. [3H]Rauwolscine also behaves as a 5-HT1A receptor agonist and this conclusion is compatible with earlier functional studies, indicating that rauwolscine (as well as yohimbine) has agonistic properties at the level of 5-HT autoreceptors[2]. When using [3H]5-HT as a radioligand, rauwolscine is determined to have relatively high affinity for the human receptor (Ki human=14.3 nM, Ki rat=35.8 nM)[3]. Saturation studies shows that the affinity of [3H]Rauwolscine is similar in mouse, rat, rabbit, dog (2.33-3.03 nM) except man where it is significantly higher (0.98 nM) [4].